1. Field of the Invention
The present invention is generally concerned with the electro-deposition of metal onto a continuously moving metal strip.
It is more particularly concerned with a method of regulating electrolytic deposition of a metal coating onto a metal strip forming a cathode and moving continuously at a given feed rate in an electrolyte past periodically disposed anodes. The anodes are supplied with direct current by respective controllable rectifiers, and the coating deposited on the strip depends on the output current of each rectifier.
2. Description of the Prior Art
One example of the use of the technique of electrodeposition of metal is the tinning of a metal strip as described in U.S. Pat. No. 4,699,694 which relates more particularly to the regulation of the deposition of metal by means of a microprocessor. This patent describes a method of regulating the quantity of metal deposited electrolytically onto a strip to be coated that moves continuously in a deposition installation including a plurality of storage tanks filled with electrolyte. The strip passes over a conductive roller forming a cathode associated with each storage tank and the coating metal is supplied by bars of said metal carried by conductive bridges and forming anodes disposed in each storage tank along part of the path of the strip in said tank.
The regulating method of the aforementioned U.S. patent consists in calculating for each displacement of the strip between two successive bridges the deposition of metal under each bridge as a function of the current intensity fed to that bridge, the strip feed rate and the efficiency of the bridge, monitoring separately each length of strip equal to the distance between two successive bridges by cumulating the successive deposits of metal, establishing the deposit balance under the last bridge carrying current in order to determine the current required under this bridge to complete the deposition of metal, determining the overall current intensity required to obtain the necessary current intensity under this final bridge, and on each acquisition of an average measurement across the entire width of the strip calculating, allowing for the transfer distance, the difference between this average value and a predetermined order value to determine a correction coefficient for the theoretical efficiency of the deposition of metal under each bridge. The method includes measuring the metal deposited on each side using a periodic scanning gauge disposed at the exit of the installation, deposition being controlled on the basis of data supplied by the gauge.
This method reduces the sensitivity of the installation to speed fluctuations, as compared with manual installations. However, a method of this kind does not totally overcome the problem of coating fluctuations.